This invention relates to drilling fluids.
It is known to add sulfonated asphalt to drilling fluids so as to improve the rheological properties thereof. Drilling fluids by their very nature present unique and rather difficult requirements. On the one hand, the fluid must be capable of exhibiting some rather sophisticated performance characteristics such as inhibiting disintegration of cuttings to just the right extent, protecting unstable shales, have lubricating characteristics and a viscosity sufficiently low to allow pumping. On the other hand, any material which is to be injected into a well in large quantities obviously has to be as inexpensive as possible.
The fact is, however, that some of the additives in drilling muds are relatively expensive, as for example, the sulfonated asphalt. It is only natural in almost every technology to try to replace an expensive ingredient with a cheaper one as a filler or extender, this being limited by the extent to which one can tolerate the poorer performance generally imparted by the filler or extender.